The present invention relates to an apparatus for synthesizing urea from ammonia and carbon dioxide at a temperature of 100.degree.-250.degree. C, and under a pressure of 100-300 kg./cm. in the presence of unreacted feed, the feed being separated from an after-synthesis alloy and recycled to a synthesis reactor.
Synthesis of urea takes place at elevated temperature and pressure according to the following reactions: EQU 2 NH.sub.3 + CO.sub.2 .fwdarw. NH.sub.4 CO.sub.2 NH.sub.2 ( 1) EQU nh.sub.4 co.sub.2 nh.sub.2 .fwdarw. co (nh.sub.2).sub.2 + h.sub.2 o (2)
reaction (1) is highly exothermic and proceeds rapidly, whereas reaction (2) is weakly endotheremic and requires a long time to attain a state of equilibrium. Consequently, reactors for the synthesis of urea have large capacities which influence considerably the costs of these reactors.
In the past, vertical cylindrical reactors for urea synthesis are constructed to have a small linear flow rate of about 1 cm./s. This results in strong circulations in the inside of the reactor because of high rate of flow of inlet streams, thermal effects of chemical reactions, and considerable differences in densities of the reaction mixture in the bottom part and the top part of the reactor. Consequently, the nature of flow is far from a piston flow, which kind of flow is advantageous for reaction (2).
It is known to use baffles of perforated plates in reactors in order to eliminate undesired circulations, cf. S. Yoshemura, Hydrocarbon Processing, 49, 6, pp. 111-115 (1970), and G. I. Nieupokajewa et al, Chim. Prom. No. 6, pp. 37-41 (1976). These baffles reduce to a certain degree linear rates in the reactor, but, due to the possibility of a bidirected flow, they do not eliminate internal circulations.